Image forming apparatuses are used as printers, facsimile machines, copiers, plotters, or multi-functional devices having two or more of the foregoing capabilities. As one type of image forming apparatus employing a liquid-ejection recording method, an inkjet recording apparatus is known that uses a recording head (liquid-droplet ejection head) for ejecting droplets of ink. During image formation, such liquid-ejection-type image forming apparatuses eject droplets of ink or other liquid from the recording head onto a recording medium to form a desired image.
As one sub type of such liquid-ejection-type image forming apparatus, a serial-type image forming apparatus is known that has a carriage mounting the recording head (liquid ejection head) serving as an image forming unit. Such a serial-type image forming apparatus forms an image by ejecting droplets from the recording head while moving the carriage mounting the recording head in a main scanning direction and intermittently feeding the recording medium in a sub-scanning direction perpendicular to the main scanning direction. Although the image forming unit is described below as the liquid ejection head, the image forming unit is not limited to the liquid ejection head and may be any other type of image forming unit.
Such a serial-type image forming apparatus typically has a main scanning mechanism (carriage scanning mechanism) to move the carriage mounting the image forming unit for scanning in the main scanning direction. The main scanning mechanism includes a driving source, a driving pulley mounted to the driving source, a driven pulley driven by rotation of the driving pulley, and an endless timing belt extended between the driving pulley and the driven pulley and serving as a carriage drawing member to draw the carriage partially fixed on the timing belt.
For example, for an image forming apparatus capable of forming images on large widths of recording media, a long-size timing belt is used as the drawing member and the carriage moves a relatively long distance during main scanning. Because a long-size endless belt compatible with image formation on large-width media costs much, it is conceivable to use an open-ended belt (i.e., belt having ends) instead of the endless belt.
However, as the main scanning distance of the carriage increases, the tension applied to the belt need be increased to stably perform the main scanning of the carriage. As a result, as the tension applied to the belt increases, end portions of the open-ended belt need be more firmly set to the carriage. In addition, the number of teeth of the belt is determined by the distance between the driving source (driving motor) and the driven pulley, and the tension of the belt is determined by the number of teeth. If the mount position of the belt to the carriage is shifted in installation, the number of teeth of the belt is changed, thus hampering application of a desired tension to the belt.